1. Field of the Invention
The present invention relates to an optical transmission line suitable for use in a Wavelength Division Multiplexing (WDM) optical transmission system, and relates to the WDM optical transmission system.
2. Description of the Related Art
A WDM optical transmission system is to transmit a plurality of multiplexed signals having different wavelengths through an optical transmission line, and can transmit a large volume of information over a long distance. Recently, there has increased a demand for an optical transmission system having a larger capacity and covering a longer distance. Preventing signal distortion is important to satisfy such a demand. From this point of view, it is desired that an absolute value of accumulated dispersion of an entire optical transmission line be small over a long distance and the optical Kerr effect be small in the optical transmission line.
Japanese Unexamined Patent Application Publication No. 9-318824 discloses an optical transmission line comprising two positive dispersion fibers and one negative dispersion fiber inserted between them. In the disclosed optical transmission line, an absolute value of accumulated dispersion of the entire optical transmission line is reduced by combination of the positive dispersion fibers and the negative dispersion fiber. Also, the positive dispersion fiber having a large effective core area is disposed in the most upstream part of the optical transmission line to prevent signal distortion caused by the optical Kerr effect.